This invention relates to a method of driving light-emitting devices which make use of radiation such as visible light or vacuum ultraviolet light generated by gas discharge for displaying characters, figures and the like or for illumination.
A large number of light-emitting devices have been known in the past which use visible light or vacuum ultraviolet light generated by gas discharges, either directly or through excitation of phosphors, for the purpose of display, illumination or the like.
As an example of the prior art, a flat gas discharge display panel using d.c. gas discharge can be mentioned. FIG. 1 is an exploded perspective view of a panel analogous to one disclosed in reference No. 1, J. H. J. Lorteije & G. H. F. de Vries, "A two-electrode-system d.c. gas-discharge panel", 1974 Conference On Display Devices and Systems, p.p. 116-118. In the drawing, reference numeral 1 represents an insulating base plate; 2 are parallel cathodes disposed on the base plate; 3 is a spacer; 4 are through-holes bored in the spacer; 5 is phosphor applied to the inner walls of the through-holes; 6 are parallel anodes disposed perpendicular to the cathodes 2; and 7 is a transparent face plate. The through-hole 4 serves as the discharge space and has a suitable gas sealed in it. A part each of the cathodes 2 and anodes 6 is exposed to the throughhole 4, forming a pair of discharge electrodes.
In other words, a discharge tube is defined by each through-hole and pair of discharge electrodes confronting each other across the through-hole. Accordingly, the panel shown in FIG. 1 is a matrix type panel in which the discharge tubes are arranged in a 3.times.4 matrix. If gas which generates vacuum ultraviolet light, such as Xe, is selected as the gas to be sealed inside, the vacuum ultraviolet light excites the phosphor 5, generating visible light.
A variety of methods for driving the panel shown in FIG. 1 are known. The method of the reference No. 1 applies a d.c. voltage between the electrodes. In a reference No. 2, i.e., G. E. Holz, "Pulsed Gas Discharge Display with Memory", Society for Information Display, Digest of Technical Papers, pp. 36-37, 1972, a pulse voltage having a width of 1.5 .mu.s and a period of 50 .mu.s, for example, is applied between the anode and cathode. Similar methods of applying the pulse voltage are also disclosed in the following references Nos. 3 through 5:
Reference No. 3 PA0 Reference No. 4 PA0 Reference No. 5
M. F. Schiekel and H. Sussenbach, "DC Pulsed Multicolor Plasma Display", Society for Information Display, Digest of Technical Papers, pp. 148-149, 1980; PA2 Y. Okamoto and M. Mizushima, "A Positive-Column Discharge Memory Panel without Current-Limiting Resistors for Color Display", IEEE Trans on Electron Devices, vol. ED-22, pp. 1778-1783, 1980; PA2 B. T. Barnes, "The Dynamic Characteristics of a Low Pressure Discharge", Phys. Rev. vol. 86, No. 3, pp. 351-358, 1952.
To panels having dielectric covers on the cathode 2 and the anode 6 of FIG. 1, a driving method of applying a.c. voltage across the electrodes is known from reference No. 6, H. J. Hoehn, "A 60 line-per-inch Plasma Display Panel", IEEE Trans. Electron Devices, vol. ED-18, pp. 659-663, 1971.
The abovementioned panels utilize the radiation from the negative glow or positive column of the d.c. or a.c. gas discharges. The problem common to these panels is that their luminous efficacy is low. Though varying to some extents depending upon the emitted colors, the efficacy of green, which shows the highest efficacy, is at most about 1 lm/W. For high luminance display, therefore, the input power is increased which raises the panel temperature, so that the panels crack due to thermal strain.
Examinations of a color television display element using the gas discharge panel have long been carried out, as disclosed, for example, in the reference No. 7, S. Mikoshiba, S. Shinada, H. Takano and M. Fukushima, "A Positive Column Discharge Memory Panel for Color TV Display", IEEE Trans. on Electron Devices, vol. ED-26, pp. 1177-1181, 1979. However, such an element has not yet been put to practical use mainly because its luminous efficacy is low. Hence, improvements in or relating to the luminous efficacy are of the utmost importance in this field of the art.